Ending PS3 support absolutely frees up resources for SE. First off it's an additional platform that needs some level of custom code developed for it for every lower level functional change. PS3 and PS4 are not compatible code-wise and there has to be some level of platform specific development occurring.

Additionally the minimum support spec always holds back software development particularly for graphically intensive software. In this case not having to work around the PS3 memory and graphics restrictions will also free up some development and quality/testing resources.

PS4 will likely still be viable for some time. Although it is only at this point equivalent to a low to mid level desktop pc it is optimized for playing video games and so has more capability in this regard than a pc of equivalent specs. It is also running a more efficient, less background intensive OS than windows. So in this respect with PS3 gone it is low end PCs that are now holding the game back (even with increased requirements for these).

Finally, all of this only frees up the opportunity for SE to use these resources in developing further enhancements for FFXIV. What they actually do with this is of course up to them and may have no impact on our game.